1. Field of the Invention
This invention relates to a rotating anticathode X-ray generating apparatus and an X-ray generating method for generating an X-ray with ultrahigh brightness.
2. Description of the Related Art
In X-ray diffraction measurement, it may be required to irradiate an X-ray with as high intensity as possible onto a sample. In this case, a conventional rotating anticathode type X-ray generating apparatus would be employed for the X-ray diffraction measurement.
The rotating anticathode X-ray generating apparatus is configured such that an electron beam is irradiated onto the outer surface of the columnar anticathode (target) in which a cooling medium is flowed while the anticathode is rotated at high speed. In comparison with a stationary target X-ray generating apparatus, the rotating anticathode X-ray generating apparatus can exhibit extreme cooling efficiency because the irradiating position of the electron beam on the anticathode changes with time. Therefore, in the rotating anticathode X-ray generating apparatus, the electron beams can be irradiated onto the anticathode in large electric current, thereby generating an X-ray with high intensity (brightness).
By the way, the intensity of the resultant X-ray generated is in proportion to the electric power (current voltage) to be applied between the cathode and the anticathode. On the other hand, since the brightness of the X-ray can be represented by (electric power)/(area of electron beams on target), the maximum value in output of the X-ray depends largely on the area of the electron beam on the target. For example, the output intensity of the X-ray can be enhanced only to 1.2 kW at a maximum in the conventional laboratory rotating Cu anticathode type X-ray generating apparatus when the electron beam is irradiated onto the target at a spot size of 0.1×1 mm, and also only to 3.5 kW at a maximum in an ultrahigh brightness rotating anticathode type X-ray generating apparatus.
In this point of view, such a technique is disclosed in Japanese Patent Application Laid-open No. 2004-172135 as irradiating the electron beam onto the inner surface of the cylindrical portion which is rotated around the center axis of the rotating anticathode X-ray generating apparatus and heating the electron beam irradiating portion beyond the melting point of the material making the cylindrical portion, thereby generating the high bright X-ray. In this case, since the electron beam irradiating portion is heated beyond the melting point of the material of the cylindrical portion, the electron beam irradiating portion is at least partially melted. However, since the electron beam irradiating portion is held on the cylindrical portion by the centrifugal force caused by the rotation of the rotating anticathode, the melted portion of the electron beam irradiating portion can not be splashed.
In the conventional technique, however, since the electron beam irradiating portion is at least partially melted through the heating beyond the melting point of the material of the cylindrical portion, the area around the electron beam irradiating portion is heated to a relatively high temperature so that the vapor pressure of the area becomes high. As a result, the rotating anticathode (cylindrical portion) is consumed remarkably so that the utilization efficiency of the rotating anticathode may be deteriorated.    [Patent Application No. 1]    Japanese Patent Application Laid-open No. 2004-172135